1. Field of the Invention
The present invention relates to a rotation sensor equipped wheel support bearing assembly for use in, for example, automotive vehicles and, more particularly, to a rotation sensor equipped wheel support bearing assembly suitably employed in a wheel support bearing assembly for the support of a vehicle driven wheel.
2. Description of the Prior Art
As a rotation sensor used in a wheel support bearing unit, a magnetic encoder type for an anti-lock brake system (ABS) has hitherto been employed widely. This is a type which makes use of a ring shaped magnetic encoder and includes a magnetic encoder, fitted to an outer periphery of a rotating side raceway ring, for example, an inner ring, and a magnetic sensor fitted to a stationary side raceway ring or a bearing end cover. (See, for example, the Patent Document 1 listed below.)
Other than the magnetic encoder type, arrangement has been suggested, in which a resolver is incorporated in a wheel support bearing assembly as a rotation sensor to detect rotation of a vehicle wheel. (See, for example, the Patent Document 2 listed below.)
On the other hand, As a rotation sensor capable of being incorporated in a small size machine and also capable of detecting a highly precise angle of rotation, the use has been suggested of a magnetic sensor array. (See, for example, the Patent Document 3 listed below.) This is of a structure in which, as shown in FIG. 7, a magnetic sensor array 45 including a plurality of magnetic sensor elements (MAGFETs) arranged in a predetermined pattern is integrated on a sensor chip 42 together with a circuit device 46 including a signal amplifying circuit, an AD converter circuit, and a digital signal processing circuit, which chip 46 is in turn arranged in face-to-face relation with a magnet 44 arranged on a rotating member 41. In this case, the magnet 44 is so designed as to have an anisotropy about the axis of rotation O and, on the sensor chip 42 referred to above, the magnetic sensor arrays 45 are arranged along each of four sides of the imaginary square shape.
With the rotation sensor 43 of the structure described above, respective outputs from the magnetic sensor arrays 45 along those four sides of the imaginary square shape are read by the signal amplifying circuit and the AD converter circuit to thereby detect a distribution of magnetic fields of the magnet 44 and, then, based on a result of such detection, the angle of rotation of the magnet 44 is calculated by the digital signal processing circuit.
A sensor IC for detecting the angle of rotation of the magnet, in which magnetic sensor elements such as, for example, Hall elements or MR elements are integrated together with processing circuits, is currently manufactured and published by some companies, although differing from a detecting method disclosed in the Patent Document 3 listed below. (Such includes, for example, a programmable magnetic rotary encoder (AS5040) available from AMS Co.) and a rotation position sensor IC (MLX90316) available from Melexis Inc.)                Patent Document 1: JP Laid-open Patent Publication No. 2006-105185, published Apr. 20, 2006.        Patent Document 2: JP Laid-open Patent Publication No. 2005-076729, published Mar. 24, 2005.        Patent Document 3: JP Laid-open Patent Publication No. 2004-037133, published Feb. 5, 2004.        
Currently mass-produced types of rotation sensors of the magnetic encoder type are merely capable of detecting the velocity of rotation, but not capable of detecting the direction of rotation. To detect the direction of rotation with this rotation sensor, it is necessary to detect two rotation signals having respective phases different from each other and, for this purpose, the use of two magnetic encoders or the use of a magnetic sensor IC in which two sensor elements are mounted in the same package, is required. In such case, problems tend to occur that not only does the space for mounting increase, but also the cost increases. Also, since the magnetic encoder is of a ring shape fitted to an outer periphery or an inner periphery of the rotating side raceway ring, this necessitates an increase of the space for mounting.
Also, a signal from an ABS sensor can be utilized in various vehicle controls including, for example, a vehicle attitude control and in such case, a signal of high resolution is desired for. With the ABS sensor of the magnetic encoder type discussed above, since the resolving power depends on the number of magnetic poles of the magnetic encoder, it is necessary to minimize the forming pitch of the magnetic poles, but since minimization of the forming pitch of the magnetic poles will result in reduction in magnetic field strength, a large sensor gap can not be secured between the magnetic encoder and the magnetic sensor, thus imposing limitations on manufacturing thereof.
Where the rotation sensor of a resolver type disclosed in the Patent Document 2 quoted above is employed, problems arise in that not only does the size tend to increase for the mounting of the sensor, but also the cost tends to increase.